1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing a semiconductor device. In particular, the present invention relates to a semiconductor device including a photoelectric conversion element.
2. Description of the Related Art
Among a variety of sensors, sensors which detect visible light with a wavelength of 400 to 700 nm are referred to as optical sensors or visible light sensors. Optical sensors or visible light sensors are known to be used for, for example, detecting optical signals to read data, detecting ambient brightness to control operation of electronic appliances, and the like.
For example, in cellular phones or television units, optical sensors are used for adjusting the luminance of display screens in accordance with the ambient brightness of places where they are set.
Such a semiconductor device typified by the optical sensor or the visible light sensor is formed in such a manner that transistors are formed over a substrate such as a glass substrate or a wafer substrate, and then the substrate is cut (divided).
In general, a step of cutting a substrate is performed as follows: a groove is formed on a surface of a substrate (referred to as scribing) with a scribing device and the substrate is cut along the groove. As a scribing method, a method using a laser is given as well as a mechanical method using a diamond cutter or the like. In the case of the method using a laser, after local application of heat with a laser, an irradiated region is rapidly quenched, so that the substrate is cracked due to thermal stress generated in the substrate. Further, a method is proposed, in which a short-pulse laser is used as a laser and a rapid quenching step is omitted to prevent the substrate from being thermally strained in the rapid quenching step (for example, see Patent Document 1: Japanese Published Patent Application No. 2007-331983).